A Libyan man investigates the inside of the U.S. Consulate after an attack that killed four Americans, including Ambassador Chris Stevens, on the night of Tuesday, Sept. 11, 2012, in Benghazi, Libya.

WASHINGTON — House Republicans on Wednesday renewed charges that the Obama administration is covering up information about last year’s deadly assault in Benghazi, Libya, drawing an angry rebuke from Democrats who accused the GOP of politicizing the issue at a jam-packed hearing.

Rep. Darrell Issa, R-Calif., chairman of the Oversight and Government Reform Committee, said the purpose of the hearing with three State Department witnesses was to get answers.

“These witnesses deserved to be heard,” Issa said.

Rep. Elijah Cummings of Maryland, the panel’s top Democrat, said he wasn’t questioning the motives of the witnesses. “I am questioning the motives of those who want to use them for political purposes,” he said.

Three State Department witnesses, including the former deputy chief in Libya, were testifying Wednesday before the panel. The hearing is the latest in a long-running and bitter dispute between the administration and congressional Republicans who have challenged the White House’s actions before and after the Benghazi attack.

The witnesses were Mark Thompson, acting deputy assistant secretary for counterterrorism; Gregory Hicks, the former deputy of mission in Libya; and Eric Nordstrom, a former regional security officer in Libya who testified before the panel in October.

On Sept. 11, 2012, two separate attacks hours apart on the U.S. facility in Benghazi killed Ambassador Chris Stevens and three other Americans. An independent panel led by former top diplomat Thomas Pickering and retired Gen. Mike Mullen concluded that management and leadership failures at the State Department led to “grossly” inadequate security at the mission. The panel’s report singled out the State Department’s Bureau of Diplomatic Security and the Bureau of Near East Affairs.

The report failed to placate GOP lawmakers, conservatives and outside groups, some of whom contend that Benghazi is comparable to the Watergate and Iran-Contra scandals and deserves a more thorough examination. Two of the outside groups — Special Operations Speaks and Special Ops OPSEC — have been raising money on the issue.

The target of much of the conservative wrath is former Secretary of State Hillary Rodham Clinton, a potential presidential candidate in 2016, who stepped down after four grueling years with very high approval ratings. In her last appearance on Capitol Hill in January, a defiant Clinton took responsibility for the department’s missteps leading up to the assault, while rejecting suggestions the administration had tried to mislead the country about the attack.

She insisted that requests for more security at the diplomatic mission in Benghazi didn’t reach her desk.

“I did not see these requests,” she said. “They did not come to me. I did not approve them. I did not deny them.”

“It looks pretty clear that there was some catastrophic decision-making that in some way contributed to the death of those four Americans,” said Rep. Mike Rogers, R-Mich., chairman of the House Intelligence Committee. “And that part I think is what the investigation will unfold.”

The Pentagon provided Congress with a timeline of the actions of security personnel and other senior officials around the attack last November, but Rep. Howard “Buck” McKeon, R-Calif., chairman of the House Armed Services Committee, said Wednesday that it was insufficient.

The Oversight committee under Issa’s tutelage is looking to its witnesses to “put forward information about Benghazi that the Obama administration has tried to suppress,” said Frederick Hill, a spokesman for the panel.

Democrats see it differently.

“It’s politics,” said Rep. Peter Welch, D-Vt., a member of the panel.

“If it’s a fair-minded question of what we could do better (on security), that would benefit us all. But if it’s intended to embarrass the president or perhaps Hillary Clinton, then it will be damaging no matter who the next secretary of state is or who the next president is,” Welch added.

Last week in Missouri, Sen. Rand Paul, R-Ky., another possible 2016 candidate, said that Clinton’s “dereliction of duty” in handling Libya should preclude her from holding office.

Committee Democrats argue that the investigation has become politicized, pointing to their exclusion from much of the Hill-based inquiry. Two Democratic staffers participated in an April 11 interview with Hicks, but the panel’s top Democrat said their efforts to find out about Thompson have been thwarted and they’ve been unable to talk to the witness.

“We have absolutely not one syllable about this guy. He’s going to appear in the committee tomorrow, we know nothing about him,” Cummings said. “That’s unprecedented.”

Cummings and other Democrats were furious about the interim report from the committees, released last month, which said senior State Department officials, including Clinton, approved reductions in security at the facilities in Benghazi. The report cited an April 19, 2012, cable that Republicans said had Clinton’s signature.

It’s standard procedure that cables from the State Department in Washington go out under the secretary’s authority and with her signature, or name, typed at the bottom, according to a five-page document put together by the State Department at the request of its senior leadership to rebut some of the claims about Benghazi.

Conservatives who are vital to the GOP in turning out the vote in midterm elections have pressured the party to act forcefully in investigating the Benghazi assault. In the House, more than 130 rank-and-file Republicans have signed onto a resolution calling for Speaker John Boehner, R-Ohio, to create a special select committee to look into the attacks, seeing the latest GOP investigation as less than satisfactory.